Any current a/c techs here?

Discussion in 'The BS Topic' started by ol' grouch, Jun 14, 2018.

  1. ol' grouch

    ol' grouch Veteran Member

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    Evansville, In.
    The /ac in the F-150 I got works but seems weak. Tomorrow after work, or possibly Saturday morning, I plan to hook my manifold gauges up and see if it needs a shot of refrigerant. What pressures should I see if it'
    s working correctly. Output temperature is 60 degrees in the shade.
     
  2. Mike N

    Mike N Administrator Staff Member Lifetime Gold Member

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    High side should be ambient temp + 100
    Low side 35 - 40.
     
  3. Knuckle Dragger

    Knuckle Dragger Administrator Staff Member Lifetime Gold Member

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    Given what else you've posted about the truck my first choice would be to suck all the Freon out, change the orifice, vacuum and refill by weight. Pressure charging is inaccurate most times, at least by me. If you can' get access to the machine a pressure check and fill as you describe is a good second option for now. Keep in mind Ford wants the pressures checked at 2000 rpm, max air setting and cab closed up. You should be getting no more than 40 degrees out of the vent, no less than 32-34.

    Here's a chart on what you want to look for:
    [​IMG]

    The pressures will tell the tale, but those truck were hard on fan clutches too.
     
  4. ol' grouch

    ol' grouch Veteran Member

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    It's not much cooler at speed on the highway. At least I have something to go by now. My NEWEST information is circa 1978 with R-12. I got out of auto repair in '84.
     
  5. tom3

    tom3 Veteran Member

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    Does the compressor cycle? (do late model Ford compressors cycle?) If so that's good, still has some refrig. in there, not contaminated. Shoot a can of R134 in it and see how it acts.
     
  6. PalmbchZ28

    PalmbchZ28 Veteran Member Gold Member

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    Knuckle Dragger is correct.... always charge by PT chart !
     
  7. ol' grouch

    ol' grouch Veteran Member

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    Evansville, In.
    It's working, just not very well. With the chart, I can service it properly. I'll see if it's a bit low. If it is, I'll add a bit. If not, I'll have a friend evacuate the system and then do some work then pump it down and recharge. I'm thinking it may just be low. I got the truck from the original owner and he said he never had any trouble. It also sat for a couple of years.
     
  8. Mike N

    Mike N Administrator Staff Member Lifetime Gold Member

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    For Phoenix, I understand where charging simply by pressure might not work....... those pressures at 90 degrees and above on your chart would scare the $hit out of me to see here, and it would most certainly be hot air out of the vents.
     
  9. Knuckle Dragger

    Knuckle Dragger Administrator Staff Member Lifetime Gold Member

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    I just rebuilt the A/C on my Buick a few weeks back. I charged via pressures because I didn't have access to the machine. Yesterday afternoon I pulled it all out and found I was just short of a pound low. I know it didn't leak so it's poor technique on my part. That's why I don't like using pressures to charge any more.

    Something I just noticed on that chart. The numbers are inaccurate for a variable rate system. It should still work for the OP but it might not be correct for the newer stuff.
     
  10. danbrennan

    danbrennan Veteran Member Lifetime Gold Member

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    I just added some R134a to my '96 Impala last week(almost 20 ounces by the weight on the can of refrigerant I used), and I noticed the low side pressure popped up and down depending on whether the compressor was on or off(still a cycling compressor in 1996, at least on my Impala). The pressure got up to the mid-30s when the compressor was on, but dropped down to around 15 with the compressor off. My question is, when they say the low side pressure should be 35-45 PSI(it was about 80 degrees outside when I charged it), they mean with the compressor on, correct? Otherwise I suppose they wouldn't say to turn the A/C to max when charging.

    So, if one knows the compressor is functioning correctly(manually apply voltage to engage the clutch I guess), it's okay to add refrigerant until the compressor does start cycling?

    Of course, if the refrigerant is low, that probably means there is a leak in the system that should be fixed. But sometimes I just want to get through the summer.
     

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